Clay mineral, also known as aluminium phyllosilicate, includes, among others, kaolinite, halloysite, illite, montmorillonite, and chlorite. It is one of the most commonly found minerals on earth.
Clay mineral has been widely used in various industrial applications. For example, in the paper industry, kaolinite, also known in raw form as kaolin, is applied as a coating composition on the surface of paper to allow for sharp photographic illustrations and vibrant color prints. In another instance, kaolinite is used as a filler in natural and synthetic rubber products to enhance their strength, abrasion resistance, and rigidity.
Yet, clay mineral, e.g., kaolinite, is usually deemed unsuitable as a material for inorganic membranes. Kaolinite's sintering temperature is no higher than 1200° C. Further, the structure of kaolinite, which comprises of randomly oriented stacking of individual flakes, makes it difficult to achieve good contact between the flakes during sintering. Consequently, as a matrix, kaolinite has a poor sinterability and a poor mechanical strength.
It would be advantageous to use clay mineral, which is abundant and thus inexpensive, to manufacture high-quality inorganic membranes.